The Third Generation Partnership project (3GPP) Release 12 introduced Long-term evolution (LTE) device to device (D2D) communication, also known as LTE sidelink or sidelink. D2D communication is a technology in which two communication devices, or user equipments (UEs), can communicate with each other with or without the support of a network. It is a Proximity Service (ProSe) which enables LTE-based devices to communicate directly with one another when the devices are in close proximity.
A pre-step for D2D communication is for a UE to discover another UE which transmits the appropriate D2D signals, a step known as synchronization. This procedure is similar to the LTE downlink cell search procedure. In synchronization, the timing information is first detected from the Primary Sidelink Synchronization Signals (PSSS). Then, the Secondary Synchronization Signal (SSSS) is used in order to obtain the physical-sidelink synchronization identity (NIDSL). Once the NIDSL has been detected by the receiving UE, the receiving UE can use the NIDSL to decode the demodulation reference signal (DMRS) and apply the sidelink reference signal received power (S-RSRP) measurement in order to report the strength of the detected sidelink.
In order to detect the NIDSL, the receiving UE correlates the received SSSS sequences with all possible local templates stored on the UE and chooses the NIDSL in accordance with the template which provides the best correlation, i.e. the highest correlation peak. However, since SSSS sequences are Pseudorandom Noise (PN) sequences, the SSSS based NIDSL detection method may fail in low signal interference noise ratio conditions because the correlation peak of the true NIDSL can be shadowed by interferences and noises. Therefore, there remains a need for a more reliable NIDSL detection method.